Abrasive blast contour machining to remove surface and near-surface crack initiation

ABSTRACT

A multi-axis machine includes a controller operable to control a nozzle which ejects a particulate material relative to a part surface to maintain a compound angle and predetermined stand off distance to remove surface and near-surface crack initiation sites.

BACKGROUND

The present disclosure claims priority to U.S. Provisional PatentDisclosure Ser. No. 61/352,483, filed Jun. 8, 2010.

The present disclosure relates to a surfacing technique, and moreparticularly to an abrasive machining technique that eliminates crackinitiation sites.

Conventional machining of alloy 718 material may introduce damage tosurface and near surface carbide particles inherent to the 718 alloy.These surface carbide particles are cracked by interaction of themachining tools and the brittle carbides. Under fatigue loadingconditions, these carbides may serve as preferential locations for crackinitiation which may limit the useful life of the material.

SUMMARY

A multi-axis machine according to an exemplary aspect of the presentdisclosure includes a controller operable to control a nozzle whichejects a particulate material, relative to a part surface to maintain acompound angle and predetermined stand off distance to remove surfaceand near-surface crack initiation sites.

A method of surface machining according to an exemplary aspect of thepresent disclosure includes removing surface and near-surface crackinitiation sites with a particulate matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed non-limitingembodiment. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a general schematic view of a multi-axis system for use withthe present disclosure;

FIG. 2 is a schematic view of a nozzle position with respect to aworkpiece to illustrate a first component of the compound angle;

FIG. 3 is a sectional view of the workpiece in FIG. 2 taken along line3-3 to illustrate a second component of the compound angle; and

FIG. 4 is a perspective view of a nozzle position with respect to anexample workpiece.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a multi-axis system 20. The system 20generally includes a particulate matter supply 22, a nozzle 24 todispense the particulate matter, a positioning apparatus 26 and acontrol 28. The nozzle 24 is located relative a workpiece W by thepositioning apparatus 26 under direction of the control 28. Theparticulate matter supply 22 in the disclosed non-limiting embodimentsupplies a 500 grit aluminum oxide powder through the nozzle 24 whichmay be a 5/16″ (7.9375 mm) diameter nozzle. The positioning apparatus 26provides multi-axis motion with variable velocity control toconsistently position the nozzle 24 relative to each surfaces S of theworkpiece W under direction of the control 28. The control 28 isutilized to implement the operational functionality of the positioningapparatus 26 to direct the nozzle 24 relative to the workpiece W. Interms of hardware architecture, the computing device can include aprocessor, memory, and one or more input and/or output (I/O) deviceinterface(s) that are communicatively coupled via a local interface. Itshould be understood that the system 20 is schematically depicted hereinwith conventional systems, however, various other configurations mayalternatively or additionally provided to effectuate the surfacemachining technique disclosed herein.

The surface machining technique disclosed herein utilizes the multi-axismotion with variable velocity control through the positioning apparatus26 to assure a uniform erosion rate is achieved upon the desiredsurfaces S of the workpiece W. The control 28 locates the nozzle 24relative to the surface S of the workpiece W at a constant compoundangle and predetermined stand off distance which is consistentlymaintained as the nozzle 24 traverses the various surfaces S1-Sn (FIGS.2 and 3) of the workpiece W. The compound angle generally includes analpha (α) and beta (β) component which may or not may not remain samerelative to each surface S1-Sn of the workpiece W (FIG. 3) depending ondesired amount of erosion at each surface of the workpiece.

As the particulate matter strikes the workpiece W, the particulatematter erodes the material to produce a surface free of the damagedlayer caused by previous conventional machining operations. That is, theprevious conventional machining operations result in a damaged layerwith surface and near-surface crack initiation sites. The surfacemachining technique disclosed herein eliminates this damaged layer toimprove the fatigue life up to ten times compared to the life ofconventionally machined alloy 718.

The surface machining technique uniformly removes high amounts ofmaterial as compared to conventional abrasive blasting processes. Inother words, rather than a surface treatment/cleaning process typical ofconventional abrasive blast processing, the disclosed surface machiningtechnique uses specific media, machining angles and gun distances toachieve tightly controlled and relatively significant material removalrates more typical of a machining processes. Material removal typical ofthe surface machining technique in one non-limiting embodiment disclosedherein is 0.002-0.003″ (0.05-0.07 mm) of material removal compared to aconventional abrasive surface treatment/cleaning process that removesonly approximately 0.0005″ (0.001 mm) of surface contaminants withlittle regard to final product size.

The material removal rate disclosed herein is for alloy 718 and may bevaried dependant on the surface damage experienced by other alloys. Thatis, use of different grit sizes and materials may be utilized to removesurface damage of any type. The surface machining technique disclosedherein has been found to remove both hard surface material conditionsand slightly distorted surface structure with equal efficiency onseveral high strength aerospace alloys, with no compromise in sizecontrol.

Since the surface machining technique enhances Low Cycle Fatigue (LCF)life, the surface machining technique disclosed herein provides for acompetitive advantage over those that use a typically-processed alloy718 part. Possible components that could necessitate enhanced LCF lifeare: different flight envelopes which increase stresses or temperatures,requirements for larger surface damage, i.e., handling damage,allowances in the field, or reverse engineering a material in a gasturbine engine program with lower life margins.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reasonthe appended claims should be studied to determine true scope andcontent.

1. A multi-axis machine comprising: a nozzle operable to eject aparticulate matter; and a controller operable to control said nozzlerelative to a part surface to maintain a compound angle andpredetermined stand off distance to remove surface and near-surfacecrack initiation sites.
 2. The multi-axis machine as recited in claim 1,wherein said nozzle directs an aluminum oxide powder at a constantpressure.
 3. The multi-axis machine as recited in claim 1, wherein saidcompound angle is never perpendicular to a workpiece surface.
 4. Themulti-axis machine as recited in claim 1, further comprising maintaininga uniform erosion rate across all features of a workpiece surface. 5.The multi-axis machine as recited in claim 4, wherein said uniformerosion rate removes at least 0.002 inches of material.
 6. A method ofsurface machining comprising: removing surface and near-surface crackinitiation sites with a particulate matter.
 7. The method as recited inclaim 6, wherein said removing comprises: maintaining a compound angleand predetermined stand off distance between a nozzle which ejects theparticulate matter and a workpiece surface.
 8. The method as recited inclaim 6, wherein said removing comprises: maintaining a uniform erosionrate across all features of a workpiece surface
 9. The method as recitedin claim 8, wherein the uniform erosion rate removes at least 0.002inches of material.
 10. The method as recited in claim 8, whereinmaintaining the uniform erosion rate comprises: moving the nozzlethrough a multi-axis motion machine with variable velocity control.